In a vehicle body, when the steering operation is performed and it is shifted to turning movement, suspension on a side of an outer wheel in turning is compressed and roll motion is started. In general, when the switchback steering is performed, a roll amount tends to increase when second or subsequent steering operation is performed than at the time of first steering operation. This is because, by the second steering operation in the switchback steering, for example, force in a returning direction (that is to say, extending direction) is generated in the suspension compressed in the first steering operation and transverse acceleration rapidly switches to an opposite direction, and the roll motion by the first steering operation suddenly shifts to the roll motion in the opposite direction to increase roll moment. At that time, yaw motion also suddenly shifts to the opposite direction in response to the second steering operation and yaw moment larger than that when the first steering operation is performed acts on the vehicle body.
The vehicle behavior controlling apparatus, which, when the yaw moment generated when such second or subsequent steering operation is performed is excessive, allows the yaw moment in the opposite direction to act on the vehicle body so as to reduce the yaw moment, thereby keeping the behavior of the vehicle in a stable state while inhibiting an excessive roll amount (roll moment), is conventionally known. The vehicle behavior controlling apparatus generates the yaw moment in the opposite direction by braking force applied to a front outer wheel in turning. At that time, the vehicle behavior controlling apparatus applies in advance a brake fluid pressure (hereinafter, referred to as “preparatory brake pressure”) to braking force generating means of the wheel, which becomes the front outer wheel in turning next, and controls such that the braking force can be applied with excellent responsiveness when the wheel actually becomes the outer wheel in turning and requires the generation of the braking force. Hereinafter, the control to apply the preparatory brake pressure is referred to as “preparatory brake pressure control”.
For example, the following patent document 1 discloses the vehicle behavior controlling apparatus of this type. The vehicle behavior controlling apparatus of the patent document 1 is configured to apply the preparatory brake pressure to the wheel, which becomes the front outer wheel in turning next along with the steering operation, to exert the light braking force thereon when the second or subsequent steering operation is performed in the switchback steering, and properly apply the braking force to generate the above-described yaw moment in the opposite direction to the wheel when this judges that the excessive yaw moment acts on the vehicle body as a result of the steering operation. In the vehicle behavior controlling apparatus, since the preparatory brake pressure is applied in advance to the wheel, which is the control target when generating the yaw moment in the opposite direction, it is possible to apply the braking force to the wheel with excellent responsiveness as necessary, and to perform the excellent stabilization control of the vehicle behavior by the yaw moment in the opposite direction thereby generated.
Also, the following patent document 2 discloses the technique to make the starting criterion to start applying the second braking force smaller than a predetermined criterion when the turning in one direction is judged in the vehicle behavior controlling apparatus to apply the first braking force to the wheel when the vehicle is judged to turn in one direction and to apply the second braking force to the wheel when this is judged to turn in another direction. According to the technique of the patent document 2, it becomes possible to apply the second braking force early when the second steering operation to turn the vehicle in another direction is performed in the switchback steering, and it is possible to stabilize the behavior of the vehicle while inhibiting the excessive roll amount.
Patent Document 1: Japanese translation of PCT international application No. 2007-513002
Patent Document 2: Japanese Patent Application Laid-open No. 2006-298212